The present invention relates to a folder feeder provided with a drum and used, for example, for withdrawing sheets and in particular printed sheets from a stack to feed the withdrawn sheets to a folder. The folder feeder comprises a first creasing wheel and a second creasing wheel that is arranged on the drum, which operates jointly with the first creasing wheel to crease the withdrawn sheets.
A folder feeder of this type is disclosed, for example, in European patent document EP-A-1 247 775 the disclosure of which is incorporated herein by reference. Printed sheets are pulled individually from a stack with a suction device and grippers and are folded on a folding sword during the continuous operation. The folded sheets are then deposited on a gathering chain where they are picked up by pushers. To obtain a sharp and if possible complete and closed fold, the pulled-off sheets are creased prior to the folding operation. The creased sheets are folded during the continuous operation on a folding sword, along the groove formed by the creasing. The quality of the fold depends on the quality of the creased groove. A creased groove that is not uniformly deep or is interrupted can result in a fold that is not sharp, is not complete, or is not closed. The folded sheets are subsequently used for producing print products such as brochures, magazines, catalogues, or books, meaning that in the final analysis, the quality of these print products also depends on the sheet fold quality.